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What are some of the bigger differences world wide in VFR charts?
While discussing Aviation Charts in this SE question, JanHudec &  Jwentin commented that VFR chart symbols are not internationally standardized - including airspace names and procedures.
What are some of the most important differences world wide compared to FAA (NOAA)?

To start this off, notice the UK chart does not provide degree marks as easily read on the compass rose around the VOR which appears to make route planning much slower and heading not as easily confirmed.

The CAA chart pictured is a 1:250000 which (in my experience) is usually used for confined flying - you might use one if you're gliding, regularly conducting local flights, or flying a helicopter in a specific area. I've never seen one used. You certainly wouldn't use one for cross country flying. This would be a fairer comparison of the chart that's usually used (1:500000) https://www.memory-map.co.uk/media/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/1/7/17_caa500.jpg

@BDLPPL Quarter-mil charts are sometimes used for cross-country flying in slower historical aircraft, where the extra landmarks are useful for navigation without radio aids, the slow speed means you don't need the area of the half-mil chart, and you're not high enough to need the airspaces marked on the half-mil chart - pretty similar to the glider flying you mention.

Related


text:
What are the 40 hours requirements for a PPL?
According to 14 CFR 61.109, a private pilot applicant must log 40 hours of flight time.

(...) that includes at least 20 hours of flight training from an authorized instructor and 10 hours of solo flight training (...)

What are the requirements for the remaining 10 hours?

There is no requirement for the remaining 10 hours, just that those 10 hours are part of your instruction/training.
So really you can read it as "a private pilot applicant must log at least 40 hours, of which 20 must be flight training from an authorized instructor and 10 hours must be solo".
How you distribute the remaining 10 are up to you and your instructor, although the vast majority of students don't find it difficult to place those hours anyway since the national average is closer to 70 hours to get a PPL.

There are also specific requirements for logging time doing certain things like solo cross-country flight, night flights, or landing at airports with a tower.  From the Wikipedia article on US Pilot Certification.

Accumulate and log a specified amount of training and experience, including the following:
  If training under Part 61, Title 14 of the Code of Federal Regulations (CFR) section 61.109, requires at least 40 hours of flight time, including 20 hours of flight with an instructor and 10 hours of solo flight (i.e., by yourself), and other requirements including cross-country flight, which include:
Solo requirements:

5 hours of solo cross-country time
One solo cross-country flight of at least 150 nmi (280 km) total distance, with full-stop landings at a minimum of three points and with one segment of the flight consisting of a straight-line distance of at least 50 nmi (93 km) between the takeoff and landing locations.
Three solo takeoffs and landings to a full stop at an airport with an operating control tower.

Night requirements:

3 hours of night flight training
10 takeoffs and 10 landings to a full stop (with each landing involving a flight in the traffic pattern) at an airport
1 cross country flight of 100 nm total distance at night

3 hours of flight training on the control and maneuvering solely by reference to instruments
3 hours of flight training for cross country flights
3 hours of flight training with an authorized instructor in preparation for the practical test, which must have been performed within the preceding 2 calendar months from the month of the test

source: Stack Exchange

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sort: votes


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Do airliner spoilers really "spoil" lift?
The two illustrations below show the typical spoiler location and the lift distribution of a wing. For comparison a third picture shows the location of spoilers on a glider.
It appears the airliner spoiler is located so it destroys very little lift but would really only contribute to drag - is this really the primary contribution spoilers have to the aerodynamics of an airliner or is there more happening here?

Typical location and size of airliner spoilers. - source

Typical lift distribution of wing. Red references have been added to show typical airliner spoiler. - source

For comparison, a glider spoiler located at the center of lift - source

The first picture looks like a deployed  trailing edge fowler type flap to me (drops down and back along a track), not a spoiler. The spoiler would be the flat plates in front of the spoiler, it is not deployed in the picture.

You modified the lift distribution diagram by adding spoilers without showing how that modifies the lift of the wing. The trailing edge of a wing controls how much lift is produced, whether you call it flow turning, circulation, or whatever.
Your diagram implies that lift is produced regardless trailing edge position. If this were true ailerons would have no effect since they only occupy the trailing quarter of the typical wing. Look at the camber line of the wing in your diagram with and without spoilers and you'll see. Flow does not turn with spoilers deployed, so you lose lift and gain a lot of drag.

source

Extending the wing flaps increases the camber or curvature of the wing, raising the maximum lift coefficient or the upper limit to the lift a wing can generate.

A spoiler of the variety shown in the first diagram works like a split flap upside down, reducing camber and maximum lift coefficient.

inverted

source

The diagram you are showing is a symmetrical vs cambered airfoil, that is not an accurate depiction of the aerodynamics of this question. This illustration suggests interaction of flaps but not spoilers. Spoilers do not change the wing geometry, flaps do.

The deployment of spoilers decambers the airfoil as the effective trailing edge of the wing moves to some position between the tip of the flap and the tip of the spoiler. The amount of decamber depends on the shape of the wing and the extension of the spoiler, so it may very well amount to neutral camber.

That may be plausible, now all that is needed is a source to confirm the theory. A leading edge slat is never shown as having shifted the leading edge down thus contributing some decreasing lift.This theory of a aerodynamic trailing edge shift has never been depicted on a diagram that I am aware of. A case could be made that the airflow over the spoiler might increase aerodynamic camber.

@jwzumwalt, the thing is that due to its inertia, the air can only navigate so sharp corner. To get from over the spoiler to the trailing edge, it would have to turn sharper than it can, so instead it flows off upward and a pocket of stagnant (and stagnant means ambient, so higher, pressure) forms behind the spoiler. This is the same principle as stall—the spoilers effectively force a stall.

@Jan Hudec - Ok, lets say the spoiler stalls the last 10% of the wing. According to the lift pressure isobar that's not much. (I agree with Pilothead & you, I just have never seen any collaborating proof and it baffles me none exists) There seems to be a lack of lift diagrams for leading edge slats, slots, and spoilers!

@jwzumwalt The front 90% depends on the last 10%. You don't get the isobars shown without the airflow deflection at the trailing edge. Again, ailerons don't work otherwise.

@Pilothead - I am not so sure the tail wags the head of a wing. The diamond shaped F104 wing sacrificed the entire last 50% of the wing for smooth flow over the first 50%.

@jwzumwalt, keep in mind that due to principle of action and reaction, the total change of momentum of the airflow is equal to the lift generated. If the air does not leave the trailing edge downward, the sum of the forces it applied to the wing was not upward (it might generate some lift in the forward part, but it generates more negative lift over the rear part, creating some upward pitching moment, but no total lift).

@jwzumwalt, regarding diamond-shaped F104 wing, that is a supersonic wing, and while supersonic lift still does follow the principle of action and reaction—because there is no escape from that anywhere in the known universe—it works very differently on the local level, because at supersonic speed, pressure changes don't propagate forward.

the spoilers also open a big hole connecting the top and bottom of the wing, which short-circuits the pressure differential and thereby destroys lift.

Good point! With all the considerations thus far, I'm inclined to believe there is no single major aerodynamic effect, rather it is multiple smaller factors that add up.

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Are there any cases on record of an aircraft crashing into an occupied air traffic control tower?
Aircraft frequently1 crash, or come close to crashing, from almost every cause imaginable, on or near airports, these being places where aircraft of all sizes take off and land and sleep with many other aircraft in close proximity, and where being a hundred feet above or below or to the left or right of where you should be has much worse consequences than it does up where the only things to hit are other aircraft (which are small targets which ATC does their best to keep at least five to ten hectofeet away from you vertically, and several miles away horizontally); this is why airports have specialised ARFF units, while your neighbourhood fire department probably doesn’t.
Usually (and hopefully, at least from the airport’s perspective), the only things that get damaged are the aircraft itself, one of the runways, and some grass, but aircraft also occasionally crash into hangars, and approach lights and ILS antennae are semiregular victims of errant aircraft.2  Surprisingly, though, I can’t seem to find any instances of an occupied ATC tower being hit by an aircraft, even though it’s a tall structure in the middle of an airport - are there any known cases of an aircraft crashing into an active tower, or have the controllers just been lucky so far?

1: Well, more frequently than they crash most other places, at least.
2: Which is why they’re made to be frangible (break apart harmlessly when struck); okay, usually frangible.

I did a search for "aircraft crash control tower" and found https://www.dailymail.co.uk/news/article-1204181/One-dead-seven-injured-plane-crashes-air-traffic-control-tower-Thailand.html straight away. Where did you search?

Slightly related-- a twin-engine aircraft crashed into an occupied "Flight Safety" company building in KICT a few years ago, causing several fatailities

I'm not sure I've ever seen the term "hectofeet" used anywhere ever

@GregHewgill: Mainly the NTSB's AAR database.  Feel free to write that up into an answer...

When I was jumping years ago a fellow skydiver managed to land in a solitary tree in the middle of an open field, so anything's possible.

I don't understand the downvote. This is a good question.

I'm voting to close this question as off-topic because it's not a realistic or personal thing, just a wild curiosity, and these tend to distract, and not attract quality answers.

@Pheric The mouse-over says "This question does not show any research effort; it is unclear or not useful". The comments show that basic research would have answered the question. And, arguably, it's not useful, either (but that seems kinda subjective).

@Harper wouldn't be wild curiosity if he was looking for accidents to research for a report on alternative airport layouts or something. We don't know why this question was asked.

@Pheric click the blue word "Sean" above.

@Harper fair enough.


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How much effect does the ground have on flight control when flying low?
In this awesome video, shot at the "Mach Loop" in Wales, F-15Cs fly down the valley, then cross a ridge very low to the ground. While it's difficult to tell from the video just how low they really are, they seem to be fairly close. How much effect on flight characteristics do the pilots feel as the ground comes up to meet them, then falls away?

To clarify a couple of points from the comments, I'm interested in any effects on flight control that are caused by flying fairly low over that ridge and through the valley (to grandmother's house we go).

I'm not quite sure that "impact" is the correct choice of word there...

Yeah, I thought about that, but not too hard... :) Feel free to modify it if/when you come up with something better.

When flying that high the ground has no effect on flight except on the pilot's mental process.

Yup, that's a better word! Thanks @JonathanWalters.

@JonathanWalters: Try saying that again with a straight face after some ridge flying in a glider!!!

@PeterKämpf Are you referring to up and downdrafts? Or are you assuming that I lack experience in low level or ridge flying and are trying to imply that my knowledge would be expanded if that were rectified?

@JonathanWalters: Both. Why else would I object to your comment?

@PeterKämpf Orographic winds are certainly a major factor affecting mountain flying; my reading of the question doesn't allow for it's inclusion, though I see others don't see it that way, which is fine. Regarding your assumptions, you amuse me but I shall hold my tongue.

@JonathanWalters: I find your ignorance less amusing than tiring. How exactly would an intelligent person read "any effect on flight controls"? Of course this would include pitch adjustments due to suddenly changing winds, wouldn't it?

Most ridge lift is not orographic, and not a major factor. Ridge lift is mostly  from thermals, but there's also convergence

At the high speed of the F-15s in the video ground effect is almost negligible. Ground effect is about the restriction of downwash by the ground, and at high speed and air density downwash is rather small. Also, the duration of close proximity to the ground is too short for ground effect to fully develop.
The biggest effect will be air turbulence. Since air will neither flow into the ground nor out of it, the vertical speed of atmospheric turbulence is greatly reduced when flying close to the ground. Also, the scale of turbulence will get smaller with proximity to the ground. While gusts may rock your wings when flying high, at very low altitude (less than one wingspan) the turbulence will average out over the wing.
When flying over a ridge, any wind speed component perpendicular to the ridge line will mean updrafts on the windward side of the ridge and downdrafts on the leeward side. This will be the strongest effect in this particular case of F-15s flying over a ridge at Mach 0.7 to 0.9.
Now back to that ground effect meme which seems to find wide agreement here: Ground effect is a stationary process which is strongest at low speed, when the downwash behind the wing is strong. In the case shown here, the aircraft is only momentarily in close proximity to the ground. The pressure field around the aircraft will never reflect that proximity because it is gone before the aerodynamics could start to react. This is completely instationary aerodynamics, and air, having mass, will take some time to respond. However, it is never given this time.

Low is of course a relative term but at a sufficiently low altitude a plane will physically experience ground effect. This generally occurs with in one wing spans length from the ground and manifests its self as reduced drag on the airframe, lower stalling speed and a general floating feeling.
In this specific case the planes appear to be flying low in a relatively mountainous area. The pilots may experience certain mountain related wind conditions while flying this low as well.

The floating feeling is in reference to the fact that it feels like the plane is floating on a cushion of air (not you floating within the airframe). Since the wings become more effective the plane has a tendency to not want to continue to decent as it enters ground effect.

Its worth it to do some low passes over the runway with a bit of power added (maybe 15% over idle) and try and hold the plane 10ft off the ground. You should be able to see the effect during that maneuver. Another things that shows it is an intentional ballon on your round out, the plane will seem to gently bounce up on the cushion of air.

Are you flying a high wing plane or low wing plane, I did my training in and now fly mainly low wing planes which can have a more pronounced ground effect response.

Ground effect is defined:

...the increased lift (force) and decreased aerodynamic drag that an aircraft's wings generate when they are close to a fixed surface.

Source: Wikipedia
The effect is that the aerodynamic drag is decreased and subsequently lift is increased giving the ability for the aircraft to fly at a lower speed than normally it could. It is also a reason why overloaded planes can get off the ground but then stall as soon as they try to get some altitude.
Ground effect happens when the aircraft is at an altitude that is less than the wingspan of the aircraft. For an F-15, this means that they would need to be within 43' of the ground. Having watched the video its difficult to determine the exact altitude but I'd hazard to say that they are more than 50' off the turf.
But the other part of your question is:

How much effect on flight characteristics do the pilots feel as the ground comes up to meet them, then falls away?

It can be significant, especially in low-wing aircraft. Speaking from a GA perspective, the controls become lighter and the airplane floats or doesn't want to touch the ground. However the composition of the surface has a large effect on this. Soft earth or water has a lesser effect than a hard surface like pavement. Passing over peaks at 250+ mph is probably going to have little effect whereas coming in to land will be much more noticeable.
There are a few fighter pilots that hang around here that may be able to tell you what it feels like in a fly-by-wire aircraft, but in a cable and pulley system its definitely noticeable. So much so that it can make an otherwise un-flyable aircraft fly. There are aircraft designed to operate solely in ground effect and has been a factor in aircraft crashes.

I'd also say that (at least in my experience) it's hard to separate the psychological effects from the actual aerodynamic ones.  Though my experience is mostly Piper Cherokee over dry lakes/sagebrush.

Ground effect is pretty non-existent at a mountain peak as it requires a flat surface or almost flat and occurs at roughly 0.5 to 1.5 times the wingspan with the wings level. But the questions is not about ground effect, but about any noticable effect on the 'flight-control' and other than wind effects there shouldn't be any

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How often do commercial flights go-around?
I've seen many references here to a flight going around, and YouTube is filled with videos of it happening, but I don't recall ever having been on a commercial flight that had an aborted landing. It might have happened when I flew as a small child, but, having been really, really excited to fly, I think I'd have remembered that.
How often do commercial flights actually abort a landing and have to make another attempt?
I'm primarily curious about US statistics, but non-US would be interesting as well.

related question about the cost of a go-around

A) Thanks, @pondlife - I was looking for "go-around", not "Abort". B) so that's how Community♦ gets involved in closing a question.

As mentioned here:

Go-arounds occur with an average rate of 1–3 per 1000 approaches.

Most of the videos on YouTube are of go-arounds because of weather. This is not a common scenario as many flights divert to other airports where weather is less severe.

Since I don't think I've flown that many times, that seems to be well within my statistical sample size for having missed it.

@FreeMan - Go-arounds and diverts are rarer for commercial flights than private. First because airlines use pilots with thousands of hours' experience flying complex aircraft under IFR, and second because the 5-10 minutes inherent in a go-around can send ripples through an entire airport's flight/gate schedule if it happens at the wrong time or the flight's already late (headwind, delayed T/O), so pilots are pressured by their companies to get it right the first time even in a crosswind.

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Since there's "Zulu" time, is there also "Alfa" time?
In talking about an upcoming flight, I was explaining that all flight planning is done in the background in Zulu time (UTC). I understand that, and it makes sense, and I know that tickets are only printed for in local time for pax convenience.
It got me thinking, though. There are 26 letters in the English alphabet, and 24 time zones around the Earth. Are all time zones given an alphabetic equivalent, skipping I and O (perhaps) so that while Zulu time is at the prime meridian, is the next time zone east Alfa time, while the next time zone west of it would be Yankee time?
I realize that this is probably tenuous here at Aviation, but it seems reasonable.

Just an aside, because it doesn't affect the main question - 24 hours does not mean 24 time zones.  Google lies when I search "how many time zones", quoting an article form India Today as the first hit.  Counts vary but 38 list time zones is a widely accepted answer (excluding daylight saving, which may not be applied uniformly). I don't know if any of these lack aviation facilities that may need to use local time. The tz timezone database contains hundreds, but represents historical changes.

@ChrisH: Some timezones have offsets of 30 and 45 minutes, not full hours. They will never be in the A-Z times which is a code for hour offsets, not timezones.

@mins "there are 24 time zones" is a quote from the question, and what I was addressing. You and I are pointing out something similar but from different directions; your 2nd sentence sum it up nicely

I used to think it was called "Zulu" because the Prime Meridian passes through Africa.

After that got you thinking, what research did you do? Why didn't you Post that here?

Thank you for your question! I really learnt something today. I always thought there's just "zulu" time and it's called like this simply because "z" is the last letter in the alphabet - basically an arbitrary decision somebody once made based on it being the "zero time" (thus "z[ulu]"). Now I learnt that there's a whole system behind it - really interesting!

There was a brief discussion on that, @RobbieGoodwin, but someone (mod-like, I'm sure) deleted the comments. Not worth repeating.

Squint for instance at https://militarybenefits.info/military-time/ If nothing else, that should remind us that there being 24 hours in a day is not enough reason to impose 24 time zones without regard to geography, culture or Lord knows what practicalities.
Who suggests time is usefully different from geography might explain why there is not one single time across the whole planet.
On the other hand, how often has drawing an "obvious" line on a map caused uproar?

Yes. From Wikipedia's List of Military Time Zones, a letter is assigned to each time zone, with Alfa representing UTC+1 and running through Yankee, UTC–12. Zulu, of course, is UTC+0. Juliet is not used and "may be used to indicate the observer's local time."
Note that there are twenty-five time zones represented in this system: twelve zones to the left of UTC, twelve to the right, and UTC itself. This system does not cover all time zones in the world, which range from UTC–12 to UTC+14—plus several in-between time zones.

Notably, this list of military "time zones" is based solely on the offset from UTC - which may not always cleanly correspond with actual time zones used in practice (due to Daylight Saving Time, and some time zones having offsets that are not in hour intervals).

Most places that to DST do it by one hour would would just move to an adjacent time zone, but I am aware of one exception.

The big question is why was Juliet skipped?

@Rock The Wikipedia article says 'to avoid confusion with "I" ', though it's uncited.

@wjandrea Thank you! I had searched the article for "Juliet" and not "J".  Now I see the note you mention.  Thanks!

@RockPaperLz-MaskitorCasket No, the big question is why aren't they laid out contiguously? Why are M and N on opposite sides of the Earth, same with Y and Z.

"this list of military "time zones" is based solely on the offset from UTC - which may not always cleanly correspond with actual time zones used in practice" Cannot emphasize this enough. My main gig is time series data, and I've spent a disturbingly high proportion of my career just untangling time zones.

Zulu for "Z" because it is the Zeroth meridian, passing through the Greenwich observatory, not necessarily because the UTC offset is zero, although this is a consequence.
Yes there is an extension based upon whole hour increments, and yes there are more than 24 time zones since some align to a half hour.
"A" was for "Atlantic Time" and "Y" was for "Yukon" time, in a mnemonic fashion, see RFC724, noting convenience of "H" for Hawaii.
RFC 733 explicitly states "J" is not used. These are but humble RFC's but ratify the convention in the digital age.
It was a US military extension. Whereas the email header +/- convention is more widely used by mail servers. It makes sense that ARPA (& Net) would follow. Aviation usage would be more informal.
Table from RFC 733 Military is taken to mean US military.
zone        = ( ["-"] ( "GMT"               ; Relative to GMT:
                                            ; North American
                 /  "NST" /                 ;  Newfoundland:-3:30
                 /  "AST" / "ADT"           ;  Atlantic: - 4/ - 3
                 /  "EST" / "EDT"           ;  Eastern:  - 5/ - 4
                 /  "CST" / "CDT"           ;  Central:  - 6/ - 5
                 /  "MST" / "MDT"           ;  Mountain: - 7/ - 6
                 /  "PST" / "PDT"           ;  Pacific:  - 8/ - 7
                 /  "YST" / "YDT"           ;  Yukon:    - 9/ - 8
                 /  "HST" / "HDT"           ;  Haw/Ala   -10/ - 9
                 /  "BST" / "BDT"           ;  Bering:   -11/ -10
                    1ALPHA       ))         ; Military: Z = GMT;
                                            ;  A:-1; (J not used)
                                            ;  M:-12; N:+1; Y:+12
            / ( ("+" / "-") 4DIGIT )        ; Local differential
                                            ;  hours/min. (HHMM)

Of course the differential format is predominantly used in email headers.

Isn't there also a :45 time zone?  Maybe Tibet?

@JoelFan Chatham Islands, New Zealand.

@JoelFan Nepal uses UTC+05:45

The German Wikipedia gives also some details about then time zones which are not full hours. However, the topic does not provide a references, so it could be false.

For time zones that differ from UTC by odd multiples of half an hour, an asterisk is added to the letter of the time zone closer to the prime meridian, and a diamond is added for a distance of 45 minutes. Examples are Newfoundland in time zone P* (UTC-03:30) or Afghanistan in time zone D* (UTC+04:30). Exceptions are the M time zones, which are more than 12 hours apart from UTC. For example, the Line Islands have a time difference of 14 hours from UTC (UTC+14:00), but are west of the International Date Line, so the time zone is marked with a cross as M†. The same exception applies to the time zones M♦ (UTC+12:45, Chatham Island) and M* (UTC+13:00, Phoenix Islands and Tonga).
Translated with www.DeepL.com/Translator

Maybe, it should be noted that these "military" time zones are actually used by the NATO and regions like Chatham Island or Tonga simply don't have so much interest for the NATO. Forces which are operating there, most like will use Zulu time.

Zulu time is also used in civil aviation.

@VladimirF yes, there is no question about it. Question is what about the other characters A to Y?

All time zones are attributed a name from the NATO phonetic alphabet, from A to Z (Z timezone being UTC).
Note that while timezone L is attributed to UTC+11, I have seen it more than once being used to represent local time (L for "local" and not Lima, I assume). While local time is supposedly coded J as per randomhead's answer and source, I have never encountered such.

This can't be true, because there are more than 24 time zones around the world.

Wernfried Domscheid: Would you elaborate about the more than 24 time zones?

authors: Vladimir F Героям слава


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Why is this low pass considered reckless and resulted in a license loss?
The first clip in the following video shows a Falcon 900X performing a low pass:

What exactly is considered reckless here and why would the pilot lose his license?

Oh yeah, that'll do it.  If he'd stayed on the runway axis, he probably would've been alright.

How do you know the pilot lost their license?

I thought that picture couldn't be a real frame from the video as the plane looks like its wing tip is barely 10 feet off the ground, but nope, it's real..

Pretty sure people only get to fly jets at treetop height when those jets have guns on them, or are at least trainers for the ones that do.

Don't sink. - At that speed, another few degrees of roll and it goes in the ground. B 52 JET AIRCRAFT CRASH At Fairchild Air Force base.

@copper.hat I'm going out on a limb here, but I'm guessing OP simply read the title of the video and took that as fact.  Certainly the pilot should expect to lose their licence after a stunt like that.

@J... Without knowing the circumstances it is impossible to judge whether or not it was reckless. ATC may have requested it for some reason.

@copper.hat ATC does not request such things, to the best of my knowledge, under ANY circumstances.  The only excuse for the pilot here would be if the aircraft was damaged and uncontrollable.

@J... Sure they do. You do not know the circumstances. I have been requested to do odd things from time to time. Such as a low level tight orbit on finals into Dublin airport. Or to abort a landing and make an immediate turn.

@copper.hat A turn before runway end and well below 400agl?  To skim right over airport buildings and other parked aircraft?!  That's just wanton recklessness.  I would be shocked if ATC requested that the pilot flew that manoeuvre.  There would have to be some pretty irregular circumstances out of sight of the camera, I would think.  But yes, I'll grant the vanishingly small probability that something else might be going on, I suppose.


text:
Do headrests considerably increase safety on aircraft?
When looking at newer GA aircraft, for example, Cessna 172s it is very obvious that the seat design has changed quite a lot over time. With the older ones having very short backrests and the newer ones being equipped with quite high seats including headrests the analogy to the automotive world is undeniable. Do the same reasons like impact safety apply to this development? Would it make sense to retrofit headrests for safety reasons?

Shoulder belts would be a better investment. I'm not sure that headrests increase safety, generally in an impact your head will move forward. It's different in a car where you can be rear ended. There's only one accident I can think of where the NTSB said a headrest would have made a difference, it was a small aircraft hitting a berm on take off.

You aren't going to get rear ended in an airplane, which is the primary safety benefit of headrests.  On the other hand, there is still some benefit to having them because in a hard forward crash, if you have shoulder harnesses on, you will probably get rebounded back into the seat to some degree or another, and the headrest will keep your head from snapping back too far during the rebound.  So better one there than not.
I've been following GA since the late 60s (I still have a FLYING magazine issue I bought at a corner store in 1969) and would say that they were mostly adopted in the 70s for "styling" purposes (keeping up with car interiors; there was a big effort to make GA airplanes as car-like as possible back then), but they aren't totally useless for protecting your neck in the right kind of crash scenario.
The really big sea-change in crash safety for GA aircraft was the adoption of shoulder harnesses, also in the 70s.  They made many crashes walk-away events that previously left you with fatal head injuries, or if you were lucky, you survived with a hamburger face.

@bogl Think "raw ground beef" not "meat and bun".

@bogl it's what happens to your face when it bounces off the panel in front of you after a hard stop with only a lap belt.


text:
Do small or regional airports have maintenance staff or companies onsite?
Do small airports or regional airports with just a couple of flights per day, maybe even from different airlines all have on-site aircraft maintenance staff? It hardly seems economical to have certified on call mechanics at most small airport? Are there regulations requiring such?
If there are not any, what happens if a hard landing is performed? From my knowledge an inspection by a mechanic is then required.

Well, the pilots known to be prone to hard landings, are sent to the airports where the maintenance staff are--

Small airports wouldn't have airline flights landing at them.

@jamesqf: How small are you talking? Tiny untowered airports get scheduled air carrier flights too; a quick look at some airline websites shows (just for example!) BTM, CDC, EAR, DIK, DRO, MTJ. From my brief survey it does look like all of those are Class-E-to-surface and do have airframe/powerplant service according to AirNav.

@randomhead: Looking at a few of yours, I would hardly call them small airport.  To pick some of my personal favorites that are small, places like Alpine County (M45), Sierraville (O79),  Ocean Ridge (E55) in California,  Gabbs (KGAB) in Nevada, Smiley Creek (U87) and Copper Basin (OU2) in Idaho... Heck, some of them are even paved :-)

@jamesqf That's neat and all but OP's question was about "small airports or regional airports with just a couple of flights per day" and it definitely sounds like the context is scheduled air carrier flights. Listing a bunch of tiny airports that may or may not have instrument approaches or even paved runways doesn't do anything except gatekeeping.

@randomhead: But you're just doing a circular argument.  And yes, there is a certain aspect of gatekeeping.  If people want to ask questions about flying as a passenger on commercial flights, then the Travel site is a better place.

For scheduled commercial aircraft you will generally find:
If enough aircraft are coming and going from a particular airport, the airline may keep a line maintenance operation running there that can handle short-term maintenance and troubleshooting, or special inspection operations.
If not, and the airport has a AMO (approved maintenance organization) on site, the airline may contract with the AMO for line maintenance services, troubleshooting or special inspections.
If that's not the case, the airline will simply fly mechanics to the airport when airplanes are AOG.  This is typical when airplanes have problems that prevent dispatch at small remote airports.
So if an airplane needs a hard landing inspection at a remote "outstation", it'll be done by local contract staff if an AMO qualified to do the inspection is there, or barring that, airline staff flown out to the site.

They generally all carry flyaway kits in the cargo area, which is mostly a box of the MMEL related items like blanking plates.  I don't think it's done much in NA or Europe, but yes flying with a mech on board on every trip was done by some Regional operators in China and other places like that.

Don’t airlines also have agreements to work on each others’ planes? Might technically fall under AMO, but IMHO worth adding.

In my experience you can often find an A&P at a lot of (but not all) airports even really small ones like KDYL where I learned to fly. However these mechanics may not have the experience or know how to work on all aircraft all the time but can likely handle most straight forward issues that could arise for the aircraft that land at the field. These mechanics may not work for the charter or airline operations based at the airport or elsewhere but are often more than capable of working on their aircraft provided the airline/charter operation permits it.
Keep in mind that at a great deal of airport there are at least a few aircraft based there (commercial or not) and all aircraft need at least an annual inspect so a mechanic is often never far off.
If local maintenance is not an option its not uncommon for mechanics to be dispatched to the field for an onsite repair.

As others have said, airlines may have line-maintenance staff on-site, either organic or contracted through an AMO of their choice. On the GA/non-airline side of things, you can almost always find an A&P or an FBO. Most airports that a regional airline would fly to, and many that receive NO scheduled airline service, have at least one FBO. Take Martin State Airport (KMTN), a Class D general aviation/reliever airport. The runway's about 7,000 feet long, so it receives quite a bit of bizjet traffic and general aviation. There are 232 aircraft based there, so there's definitely maintenance, between the FBO and the A-10 squadron based on the field. Don't expect to land your J3 Cub and get maintenance from the A-10 guys, but they count as maintenance on-site. According to AirNav, you'll find minor airframe and powerplant service, but no oxygen of any kind. It's a rare airport that has absolutely NO maintenance personnel on-site, even if they're private A&Ps not working for the airport, but I'm sure they exist. Small bush strips (debatable whether or not you can truly call that an airport) might not- the one that comes to mind is Trent Palmer's runway outside his house- he's not an A&P, so no MX on-site. However, it's certainly more common that there's maintenance on the field than not.

Airports usually do not hire maintenance staff for other than maintaining the airport facilities. Companies (Airlines, FBOs) that operate there will usually have a base and have the required staff on site. If you land at an airfield where there is an established FBO and you ding your plane, you could ask them to repair it, if it falls within their operating certification. Otherwise you will have to solicit the services of an organisation based elsewhere.


text:
Factors to be considered when re-engining aircraft
What parts of the aircraft need to be adjusted / refitted / added when fitting new (different type) of engines?
Also what what kind of re-certification regarding airworthiness etc. will be necessary?

This may depend a great deal on how different the engines are. Could range anywhere from basically no changes to huge redesign. Did you have any specific case in mind?

Thanks for the comment, the question just popped up when i was heard about the B-52 and then started thinking about how it would for example be done for the A340-600

This depends greatly on the engine. However, given the 737 MAX situation, I'll assume you mean re-engining with larger, more efficient engines. This still leaves a lot of room for interpretation- what aircraft are we working with? Something like the 757, with tons of ground clearance? Or something like the 737, with very little clearance? I'll answer both.
In the first scenario, re-engining a 757, there's not a WHOLE lot that needs to be changed. The engine mount/pylon, wing structure (to account for a heavier engine), and maybe the FADEC. That's really all I can think of. Maybe the fuel system.
The second scenario is where things get interesting. If you want to avoid a 737 MAX style situation, you'll need to extend the landing gear legs and find some way to stow them. If you can't find anywhere on the airframe that's beefy enough to accept that, then you'll have to find an ideal spot and reinforce it. Then change everything that I mentioned in the first scenario.
I'm no aerospace engineer, and I'm sure I'm missing countless things here, but these are all the major things that I can think of.


text:
How would the FAA catch people without licenses?
It is know that the FAA conducts ramp checks at airports. However, is it likely to be caught flying without a license from uncontrolled airports or grass strips? If so, how would one be caught?

If they are conducting a ramp check and you don’t have a license, the chances of getting caught are 100%.  The size of the airport, the presence of a control tower, or the surface of the runway is immaterial - if it is a public airport the FAA could be there.
If they are not conducting ramp checks, you would only be caught if there were a reportable incident that brings your activity to their attention.  (airspace violation, noise complaint or tip, mishap, etc.) Otherwise, how would they know?
I’m not sure how it might work at a private airport, but I would imagine the FAA would be held to the same standards as law enforcement; i.e. they would require either consent, probable cause, or a warrant to enter your property.


text:
Why does some "Fighter Jets" have "Pitch changers" on the front?
F15 with "Pitch Changers":

The J20 with "Pitch Changers":

Now, it looks odd when you see a plane with "Pitch Changers" on the front.
So what are they and why they are on the front in the J20 ? Does that configuration effect the "Dogfight Performance" ?

Both airplanes have the vertical stabilizer(s) on the back. Perhaps you are referring to to elevator, or horizontal stabilizer. In the J-20 case it's a canard.

When the elevator is on the front, it's not a stabilizer any more because it destabilizes the airplane.

Wait a minute please, It will take me to edit the photos

OK I Revised the Q

The items you pointed out on the J-20 are canards. They are usually combined with delta wings, to alleviate some of the drawbacks of the delta.
Its main purpose is similar to the horizontal tailplane, but the canard can provide lift as well.
Depending on the aircraft, canards can be fixed or movable.

Pitch control in a canard type may be achieved either by the canard surface, as on the control-canard or in the same way as a tailless aircraft, by control surfaces at the rear of the main wing, as on the Saab Viggen.

On the J-20, the canards seem to be movable:

One important design criterion for the J-20 describes high instability.[26][27] This requires sustained pitch authority at a high angle of attack, in which a conventional tail-plane would lose effectiveness due to stalling. On the other hand, a canard can deflect opposite to the angle of attack, avoiding stall and thereby maintaining control.[28] A canard design is also known to provide good supersonic performance, excellent supersonic and transonic turn performance, and improved short-field landing performance compared to the conventional delta wing design.[29][30]


text:
What are the types of these 3 single-engine aircraft and one Multi engine aircraft?

Here are several photos of older aircraft I'd like help in naming. Year, Model, & Manufacturer.
Thanks so much.
Ron

Short note; the lower left aircraft is a twin.

I did note that after I put up the photo but still would like help ID'ing all these.

Any info on when/where the photos were taken? Just curious.

No idea, though they were purchased in N.Texas.

The upper left one looks like a Fairchild PT-19-family monoplane trainer. Production on these started in 1939 and served through the end of the war as a basic trainer. Yours might just be the PT-19B variant, which has a hood over the front cockpit and was used for instrument training:

The upper right one looks like a Vultee BT-13 or BT-15 "Valiant" basic trainer, which were used as Air Force and Navy basic trainers from 1940 to 1944:

The lower left is actually a twin-engine plane, not a single, looks like a variant of the Beechcraft Model 18, or "Twin Beech". These were built beginning around 1937 and continued well into the Vietnam years. Military designations include the C-45 Expeditor, AT-7 Navigator, and AT-11 Kansan, but your specific example appears to be civilian:

The lower right is a North American T-6 or AT-6 Texan. Production on these began in 1933 and they were only retired from all air forces in 1996 (though the last operator, South Africa, only kept them as basic trainers because a military embargo related to its Apartheid policy prevented them buying anything newer):

As far as exact build dates of these aircraft, you might be able to look up the tail numbers of each airplane, but these craft were so common and so varied during their production that exactly when a specific airframe was built is difficult to determine by looking at it. All of these aircraft, in addition, seem to have been "civilianized" after service with the USAAC/USAAF, so their full history may be very hard to trace without their logbooks.

@fooot I concur and have edited, though I think it's actually the PT-19; same airframe, but inline instead of radial engine.

You guys are terrific..Thanks!

Although these designations are probably correct, they might also be variants, like an SNJ instead of a T-6

From left to right, top to bottom, and from memory I'm guessing a Fairchild PT-19, a BT-13, a Beech D18, and a North American AT-6. The BT-13 had a 450 horse P&W. which they'd pull off that airplane and put on Stearman to make a duster/spray plane out of. All of these airplanes were really cheap after WW2.
As I remember, AT-6s sold after the war for as little as 500 USD, but then when the Korea War came along, the government wanted them back and were paying up to 30,000 for them.

I think the upper left is the older PT-19 variant; the PT-23s had a radial engine, while this one has an inline.

@KeithS You're right, and I changed the answer. I seem to remember some PT-19s having fully enclosed cockpits. I think the inline engine shown is a  Ranger engine, which were also in the Grumman Widgeon.

@Terry - The PT-26 was the variant that had the inline engine and enclosed cockpits. The engine cowling looks very similar between the two, I'm not sure if the 19 and 26 used the same engine.

The lower left picture shows a Beech 18 Twin Beech, built in the 1930's.
On the tail the markings N and 15 are visible. Since all other aircraft show registrations starting with NC and they all feature the same control tower (apart from the top left picture) I assume all photo's are from the same year. It is likely the registration of the Beech 18 starts with NC too. The only Beech 18 Twin Beech in this production list with a NC registration is the first ever built, with registration NC15810.
The lower right picture shows a North American Texan Yale, registration NC61032. It is listed in this production list.

I appreciate this information....it really helps.

The first is a Fairchild PT-19 trainer (~1940). The second looks like a Vultee BT-13 or BT-15 (~1940). The third looks like an AT-11 (~1937), and the forth is an early T-6 or AT-6A (~1937).

authors: Никита Екимов


text:
Under what circumstances should the pilot not flying intervene without asking for aircraft control?
The communication between the captain and first officer is of great importance, especially when it comes to agreeing who is the pilot flying. This question asks for the procedures regarding taking/handing over control and this is also a related question.
Neither of these question discuss under what circumstances the pilot not flying should intervene without verbally announcing their control of the aircraft.

Are there defined procedures for this?
Is seniority sufficient to immediately intervene in some situations?
Is it up to the crew to decide before-hand that the captain is allowed to "help" a less experienced first officer?

In this video (at about 1:40), the first officer is landing the plane, and immediately after touch-down the captain intervenes by pushing the stick forward, apparently without being the pilot flying at the moment.
This document is also related, although it focuses on when and how to intervene being the less experienced co-pilot. Key quote:

"You are damned if you ignore a Captain's mistakes!
You are damned if you do or say something about them!"

See http://aviation.stackexchange.com/a/5093/69.  There should always be a verbal exchange for the reasons noted in my answer to that question, however that doesn't mean that you have to wait for a response before taking control if there is a safety concern.

On some aircraft, its just not possible without positive transfer. Air France 447 is a good example, the Captain thought he was at the controls, but the FO was still holding back on the stick overriding him. The controls are not linked, so the Captain didn't know.

@RonBeyer Not true. http://aviation.stackexchange.com/questions/3455/why-is-the-priority-takeover-button-used.  It was one of the series of CRM failures that the Captain did not take control.

IANAP: At the time you indicate, the pilots are no longer "flying" the aircraft.

@CGCampbell I thought you were, by definition (kind of), "flying" the aircraft until reaching more or less full stop.

@Lnafziger Interesting. What can you say about the video I linked to? The captain says "Spoilers deployed" and then pushes the stick forward. Maybe the flight officer is in training (although the video doesn't give the impression that this is the case)?

That wouldn't be considered taking control of the aircraft.  It is most likely their SOP (standard operating procedure) for the non-flying pilot to push forward on the yoke after landing in order to improve directional control.

Document is a dead link.

@Joshua Thanks, edited.

There is transfer of control -- "I have the aircraft" / "You have the aircraft."  Then there is intervening -- which may or may not involve a transfer of control... directing "you're getting slow, ADD POWER NOW" may be a more effective example of intervening than taking control, depending on the phase of flight & other circumstances.  (It's easier for a First Officer to intervene with a directive "add power" or "go around" than than for him to take the aircraft!)  And then there is what was shown in the video, which looks like neither of the above -- simply crew duties as @Lnafziger commented. The captain there didn't take over control (yet -- the video ends before he takes over to taxi), they simply both pushed forward on the control column -- put weight on the nosewheel for better steering, perhaps.  Looked perfectly normal & expected.
To answer the question as asked ("Under what circumstances should the pilot not flying intervene without asking for aircraft control?"), there are plenty of times when intervening without taking control could be appropriate -- the directive callout ("ADD POWER!"), or correcting an aircraft system or Flight Management Computer setting, for example.  There are also a smaller set of times when "I have the aircraft!" is appropriate: a disoriented pilot is about to fly into an unusual attitude, or a pilot is incapacitated in a phase of flight where there is no time for "hey, are you okay?" to differentiate between distracted & incapacitated.  The captain always has the prerogative to take over, although there are plenty of times when something else is a better choice -- directing "go around" instead of taking the aircraft at low altitude to try & salvage a bad landing, for instance.  Particularly in cases of incapacitation, the FO also has that option, but realistically, he may have more explaining to do than the captain would have if roles were reversed.
In a pure training situation (initial formation flying in the military comes to mind), there are times when control may transfer back & forth... the student flies as far as he can, starts to get out of position, the instructor takes the aircraft, puts it back into position, the student is given control again, etc.  But that's not really the sort of scenario you'd see in airline operations.  There might be times the pilot-monitoring captain (i.e. he is the pilot not-flying on the FO's leg) might take over the FMC programming rather than talking the FO through the necessary changes -- sometimes it's just better to do it & explain what you're doing rather than talk through each entry and button press.  But that's again not really the same as "I have the aircraft."
With qualified crews in the airline world, it just isn't all that common that a situation arises where one pilot has to assume control outside of the normal transfers (i.e. the normal transfer to the captain on landing if he has the only nosewheel steering tiller).
And, as noted in the comments, every transfer, both expected and unexpected, needs to be verbalized by both pilots: "I have the aircraft."  "You have the aircraft."


text:
Costa Rica landing in the news, concerns to be taken seriously?
A landing in Costa Rica has recently caught some attention in media, for example here.
A flight from Madrid to San Jose allegedly experienced difficult winds and the pilots changed the descent pattern accordingly.
They approached the runway at a very low altitude, scaring both passengers and people on the ground. And considering the footage available in the article, I don't blame them.
The authorities however claim that this was a normal and controlled landing, and that there are no limits how low the approach is allowed to be over the area close to the runway. They admitted, though: "Sure it could have been a little higher, but the altitude and angle of the plane was fine."
Are the authorities right about this, or should the media's, the passengers' and the locals' concerns be taken seriously?

if "the media" is the dailymail, well....

Nothing in the Aviation Herald, so probably a routine landing.

For those that want to see the video without clicking the Daily Mail article: In the article, they show a short video credited to "YouTube/Johnny Vega". It appears to be taken from this longer video: https://www.youtube.com/watch?v=QNVqgUhmyU4 (the interesting part starts at 0:48).

I would like to point out a few things in your source.
First, look at the bottom right picture. It shows an altitude of about 30 feet, guessing that an average airport fence is about 9 feet high (forgive me if I'm a little bit off, I usually use SI units). Then, if you look more closely, you see that the plane is not actually right above the fence at that point, but quite a bit past it, which means that it was higher when it passed the fence. So, no big problem there.
Then the pictures of the bottom of the airplane. You notice how the airplane looks very distorted, like it has a massive nose. This is because smartphone cameras generally have wide-angle lenses - an extreme example would be a fish-eye lens. They severely distort the intuitive concept of distances (closer looks VERY close, further away looks VERY far away)- if you try to inspect it a little bit more carefully, suddenly you realize the plane is about 4-5 times the height of the quite large tree in the center of the picture. Again, no big problem.
Then there's the picture of the plane going over the road. This is shot with a narrow angle lens (probably a good zoom lens or even a telephoto lens). This has the opposite effect of a wide-angle lens: things that are in reality separated a lot look really close to each other - my favorite example being this picture. So, while it looks like it's directly at the top of the hill, in reality it's probably much further away.
Then, finally: even if all of the above were false, it still wouldn't be a big problem. A stabilized approach is a stabilized approach. A lower glide angle makes some things quite a bit easier: your engines are spooled up higher which makes them more reactive, and your touchdown will be smoother than Mick Jagger's moves. Downsides: more fuel consumption, more noise and usually more turbulent winds, which was specifically not the case according to the story (indeed, they went low to avoid those winds).

9 ft = 3 m; I'd say the fence is probably a bit lower. Still, plenty of room there (in the left image the shadow of the aircraft is over the road, but note the solar flare at the top of the picture indicating the shadow is likely quite a bit closer than the object casting it).

I actually guessed 3 m, since fences around airfields tend to be a little more serious than for keeping bunnies out. Then again, I live near an airport that doubles as a military base, so that might have something to do with my guess. I also noted the shadow, but I wasn't sure about the flares since it's filmed with a potato.

smoother than Mick Jagger's moves +1 just because

Please don't link to media articles in the general press, but especially not the Daily Mail who generally don't worry too much about facts and have no-one on staff who has a clue about aviation ("activate their tyres in time", "With its landing gear ejected, the plane comes perilously close to hitting ground level too early").
Just look at the rhetoric in the wording of the article body.  It ticks all the boxes:

...within a few feet of terrified drivers...
...Shocked passengers on board...
...eye-catching video...

The Daily Mail tries to get at least one of these a month as clickbait and for comments.
Some critical thinking.

...grazed perimeter fence...

No evidence presented.

...why so many photos...

Because the road is right at the end of the runway and spotters gather there to take such photos.

...passengers shocked...

No evidence presented and most passengers are the worst possible judges of a good approach or not. How would they know?

...how low was it at the threshold?...

No evidence presented.

...airport authorities insist it was a normal and 'controlled landing'...

What evidence is there that it was not?
SJO is known for its tricky and low approaches.  Nothing to see here.

Oh, I'd use all my votes to upvote this some more!

@Federico Thanks for the edit.  I'm normally good with my apostophes but it just so happened that I edited at the same time as you and my edit came in second.

@Simon no problem at all, I figured as much, I just left that comment in the hope to make the double edit a little humorous, but I am afraid I failed.

I totally agree with this assessment, the daily mail is a british paper famous for trying to get as many uses of "shocking", "perilous", "dangerous", and other emotive words into their articles as they can. I treat everything that paper says with suspicion.

The Daily Mail is Britain's USA Today of aviation journalism/

Please do not use code formatting for quotes. It messes things up mightily for those using non-visual browsers (e.g. screenreaders for the blind). These programs tend to read out code letter-by-letter, which will make this answer unbelievably tedious for such users. Quotation marks or quoteboxes are the appropriate ways to quote text.

@KRyan I wasn't aware of that.  Thank you for the edit and for teaching me something.

If the Daily Mail said the sun was rising in the east, I'd stick my head out the window to confirm it.

Compare and contrast


text:
Why isn't runway 4L/22R at KMDW available as an emergency runway?
Chicago-Midway (MDW/KMDW) has five runways, oriented along the diagonals of the square airport.  The longest two (13C/31C [1988 x 46 m] and 4R/22L [1964 x 46 m]) are ILS-equipped, and serve as the airport's primary air carrier runways; the other three (4L/22R, 13L/31R, and 13R/31L) are used primarily for small general-aviation operations.  Of the three, 13L/31R and 13R/31L are available for use by larger aircraft in case of emergency:

Chicago Midway International Airport covers just over one square mile (650 acres or 260 hectares) [...] and has five runways: [...]

13C/31C: 6,522 ft × 150 ft (1,988 m × 46 m), air carrier runway, ILS-equipped.
4R/22L: 6,445 ft × 150 ft (1,964 m × 46 m), air carrier runway, ILS-equipped.
4L/22R: 5,507 ft × 150 ft (1,679 m × 46 m), general aviation and air taxi.
13L/31R: 5,141 ft × 150 ft (1,567 m × 46 m), general aviation and air taxi. Used as an Emergency Runway for commercial aircraft.
13R/31L: 3,859 ft × 60 ft (1,176 m × 18 m), light aircraft only. Used as an Emergency Runway for commercial aircraft.

4L/22R, however, is apparently not available for use by air carrier aircraft even in an emergency, despite being longer than either of the other two general-aviation runways (and also twice and half again as wide as 13R/31L, the smallest runway at the airport), and the only one of the three to be useable when the winds are blowing along a northeast-southwest axis (the two designated emergency runways are both oriented northwest-southeast).
Why are Midway's two smallest runways available as emergency runways for large aircraft, but not the larger 4L/22R?
EDIT: As @RonBeyer suggests in his comment, one potential reason a runway of sufficient size might be unuseable for large aircraft could be if its bearing strength were insufficient (such that the pavement could collapse under the weight of a heavily-loaded jetliner).  However, to hear it straight from the horse's mouth, 4L/22R is rated for aircraft imposing pavement loads of up to 30 short tons per single wheel, or 60 short tons per two-wheel bogie; although not up to the standards of the airport's two air carrier runways (each rated to 47.5 short tons per single wheel, 82.5 short tons per two-wheel bogie, or 125 short tons per four-wheel bogie) or emergency runway 13L/31R (rated to 40 short tons per single wheel, or 62.5 short tons per two-wheel bogie), it far surpasses the mediocre strength of runway 13R/31L, which is rated for a mere 6.25 short tons per single wheel... and is, nevertheless, a designated air-carrier emergency runway!

4L/22R is an asphalt runway unlike the others that are concrete. It has half the load carrying capability of the concrete runways. It also does not have an EMAS system installed unlike 4R and the other runways, so I'm guessing the safety overrun areas are not up to spec for that.

If it were weight bearing capacity, why is Runway 13R/31L (PCN 42 /R/B/X/T Single wheel: 12.5) available but Runway 4L/22R (PCN 69 /F/D/X/T Single wheel: 60.0 Double wheel: 120.0) is not?

Why does it not seem odd to you that 4R & 31C also lack that designation?

@RalphJ: Because those two are explicitly designated as the airport's main air carrier runways, as opposed to being emergency-only runways, while 4L/22R isn't.  (Regardless, I see the point made in your answer.)

My current Jeppesen chart has the same "air carrier" note for 4L as for the 31 L + R.

I'm voting to close this question because it asks "why is X" when X is not, in fact, true.

@RalphJ: A scan of said chart would be an excellent addition to your answer.

@Sean It would also be a violation of copyright. No thanks.

@RalphJ: It's called fair use.  Not a violation.

Prologue: the quote in the question is from Wikipedia, and the parts there that mention the designation to commercial aircraft emergencies have later been marked as "citation needed". Therefore, for as long as an authoritative source can not be verified, it might well be that in reality there is no such designation.
Actually, should the nature of the emergency require, any runway (or even taxiway) on any airport is available for any aircraft if the crew so wishes. Some more or less famous examples of such situations (Air Safety Network):
Air Canada flight 143 (The Gimli glider, fuel starvation)
United Airlines flight 232 (Sioux City, total loss of hydraulics)
Air Astana flight 1388 (Portugal, reversed aileron cables)
If you are out of fuel or experiencing severe control issues or something of such magnitude, regardless of what you are flying there is no way ATC is going to tell you "sorry you can't land on the 4L, turn to heading..."
This might seem like splitting hairs, but that's how it is. To state that some runway is (or is not) available for emergencies of a certain aircraft type, is somewhat of a moot point.
After you've spoken the three magic words, the ATC has to, and more importantly, they want to do everything they possibly can and more to help you out. You are finally free as a bird, if only you did't have an emergency to deal with...
Speaking of splitting hairs, Gimli glider did not land in an airport at all, but it's the most famous case of the sort...

While I completely agree with this answer, it doesn't seem to answer the question of why some of the runways at KDMW are designated as "emergency runways"

@J.Hougaard  the anwer lies in the fact that runways cannot be designated as emergency / non emergency runways.

Again, I agree. But whoever wrote the quote in the question seems to think otherwise. I assume they got that idea from somewhere

Oh, checked out the source (Wikipedia), as I should have done in the first place, and the quoted stuff there about emegency use is not from a verified source. So as this is the internet... well we all know.

Yep I just added the "Citation needed" tag myself a few minutes ago. Been digging around a bit, can't fint the source of those claims. Likely written by someone with limited understanding of the subject

Ok, I better update my answer once more not  to indirectly blame the OP of missquoting...

The gimli glider did land at an airport, it just so happens that the airport was converted into a drag strip. It was an airport before that.

Yes, and the hair is now split twice

The other two 31's (not 31C) are "emergency use only" for large jets. They won't be used for anything but an emergency. While 4R is the usual runway used in that direction, 4L could be used in other-than-emergency cases. That's why it lacks the notation mentioned.
How does that matter? Let's say 31C is closed for repairs. Absent a compelling emergency, big jets won't use 31R or 31L. However, if 4R were similarly closed, 4L could be used as normal ops, as long as the aircraft performance allowed.

Why is 4L/22R useable as a spare non-emergency runway, but not 13L/31R (which is almost as long as 4L/22R, has a significantly higher weight-bearing strength, and would allow almost-normal operations with 13C/31C and 4R/22L both closed, even if the winds are running along a northwest-southeast axis [instead of the northeast-southwest axis supported by 4L/22R])?

Can you give a source for the 31's being emergency use only, as the source in the question has no source, if you get what I'm getting at?

@Jpe61 No. I'm explaining what the text quoted in the question means. As your answer points out, everything is available for emergency use; the quoted text means that those runways are only available in that case to large aircraft.

@Sean  Probably 31R's length, and the fact that it's too so close to 31C.

Ok, so your answer is just an interpretation without verification?

@Jpe61 Just adding some context from the world that I work in to the text that somebody else posted. See my comment above from my Jeppesen manual if you need something "sourced". (Though I won't be posting a screenshot of a copyrighted product.)

Does Jepp mention the "Used as an Emergency Runway for commercial aircraft"? Sorry, don't mean to harras you with this, I just hate it when Wiki has stuff like this with poor, or god forbid, no citation. People are lost enough without the internet being full of alternetive facts.

2009 Jepp plates for KMDW are available on the internet, and  they do not have any mention of emergency use of any runway.

Citation needed. Where does it say that any runways are emergency use only?

@EdwardFalk The original post is what I'm addressing here. To the extent that it is "citation needed", I'd suggest voting to close the question.

Edited Wikipedia to show that the last three runways are only available to large aircraft in emergency. The actual rule is no scheduled flights over 9 passengers and no unscheduled commercial flights 31 passengers or more. Reference is the Chart Supplement, but of course that updates frequently so there's no good way to reference it except to say "type MDW into this web form".
This is what the chart supplement says (7 OCT 2021 to 2 DEC 2021):

AIRPORT REMARKS: Attended continuously. Birds on and invof arpt. Arpt CLOSED to solo student trng. Rwy 13R–31L, Rwy 13L–31R and Rwy 04L–22R not avbl for skedd acr opns with more than 9 psgr seats or unscheduled acr at least 31 psgr seats [...] [emphasis added]


text:
What does "ENG 2 REV PRESSURIZED" ECAM message mean in the Airbus A32F?
What does "ENG 2 REV PRESSURIZED" ECAM message mean in the A32F (Airbus A320 Freighter)?
What are the possible consequences and actions the crew should take, on ground and during the flight?

What does the checklist indicate to be the proper course of action?

In case of Airbus A320 (A318/319/320/321) models, ENG 2 REV PRESSURIZED means that the thrust reverser system is pressurized. From FCOM:

ENG 1(2) REV PRESSURIZED
Reverser system is pressurized, while rev doors are stowed and locked with no deploy order.

The crew are expected to reduce the engine thrust to idle when possible in flight (also on ground).

Reverse thrust system is pressurized with reverser doors stowed and locked.
THR LEVER 1 (2) .................................. IDLE
lf flight conditions permit, reduce the thrust of the affected engine to IDLE as a precautionary measure.

You can see a case where this warning came on.
Deployment of thrust reversers in flight could have fatal consequences as seen in a B767 Lauda Air Flight 004 (note that the warning is about reverser pressurization, not deployment).

If it were reverser deployment then probably too late to see the warning anyways. :)

@curious_cat Yes. As an aside, then you'll have a REV UNLOCKED warning probably- though I doubt it'll be of any help.


text:
Why are there no commercial supersonic flights at present?
I'd think that on certain heavily trafficked routes, especially ones with lots of business travelers, there would be a market for high-speed (supersonic) flights?
Why are there currently no supersonic commercial flights? (Or are there?)

@vasin1987 http://www.telegraph.co.uk/finance/newsbysector/industry/engineering/11782446/Concorde-Mark-2-Airbus-files-plans-for-new-supersonic-jet.html

The problem is the sonic boom which is currently forbidden over and around land areas in some countries including the US. The sonic boom is continuous when the aircraft is supersonic. This restrict the supersonic flight to oceans. It seems this is not commercially profitable, considering the operational costs.

The last sentence of the highest voted answer on the Concord I think has the best reason: "BA realized that it could make more money carrying passengers subsonically across the Atlantic." Developing and flying supersonic aircraft is almost certainly not as cost-effective as sub-sonic aircraft, and there is likely just not a market for high-cost flights that are only 50% shorter.

They are working on a supersonic business jet on which Airbus is acting as a consultant and helping with the design:
http://www.aerionsupersonic.com/

If you think this is a duplicate, can you please explain why? It might be about the same thing as another question, but if it's not asking the same question or raising the same answers, it's not a duplicate.

You make two major assumptions in your question 1) there is a significant market demand for supersonic airliners 2) technology and regulation has changed since the Concorde.  While making big assumptions isn't against the rules, your question would be much more convincing and accurate if you justified them.

@CodyP please note that each of my sentences end with a question mark. They feature what "I'd think" which is indeed only assumptions. I leave confirming or refuting such assumptions to actual answers.

@Fiksdal I know.  I'm not saying the question is incorrect, or unprecedented, but you risk sounding silly if those assumptions turn out to be largely unfounded.  For example, a question about "why don't they build cathedrals anymore" is a lot more interesting if you do some research and back up exactly why people still want to build cathedrals.

@CodyP That's OK, I don't mind sounding silly at all.

You can rent warbirds in a few countries, including russia, and fly supersonic. In a sense, it's commercial :)

@Antzi Decommissioned military jets? How do you get a license to fly those?

@Fiksdal the pilot is provided. Ex: http://www.flymigsokol.com

@antzi That's pretty cool

There a several reasons for the demise of commercial supersonic aircraft.  And there is a strong possibility we may be able to take a ride on a supersonic aircraft by 2021.
Supersonic commercial aircraft have a lot of constraints on them which are not present on subsonic commercial aircraft and which military aircraft are not subject to.

Prohibitive Development Costs
Supersonic aircraft - and in particular high supersonic and hypersonic aircraft - are considerably more expensive to design and manufacture as they require the use of novel materials and manufacturing techniques in their design.  As you pass about Mach 2, heat starts to become a major problem, weakening traditional aerospace aluminum alloys to the point that they are no longer a viable material to construct an aircraft from.  The airframes also expand and contract considerably in the heat and this must be accounted for in the design.  Designers are forced to seek out more exotic materials like Titanium alloys, high temperature composites, etc.  and it is not just structure that requires novel materials to address this - fuel systems, electrical wiring, mission systems, even sealants and paint all must be chosen so as to combat heat but still satisfy traditional design metrics like safety, durability, and economics.
The result of this are very high development costs:  Adjusted for inflation, Concorde costs the governments of England and France some $28 billion or roughly 5 1/2 times the cost that Boeing spent to develop the 747.  Similar figures were consumed on the design and development of the ill fated Boeing 2707, which never progressed past the mockup stage, even after re-design.
Limited Cabin Capacities
Super Sonic Transport (or SST) design favors a slender, needle-like fuselage which limits the number of people which the jet can carry.  The Concorde was limited to approximately 100 passenger in very narrow seats; the 2707 could carry 260 people but had a length of over 300 feet making it very awkward and unruly in existing terminal aprons or taxiways.  This also makes the SST very unprofitable for its operators, as Concorde proved.  Over the last 50 years no more than 20 SSTs have ever been operational and all with only three airlines - British Airways, Air France, and the Soviet Aeroflot - all of which were heavily subsidized by their respective governments.
Propulsion Inefficiencies Restrict Range
Design of SSTs have in the past been hampered by the high fuel consumption rates of turbojet engine imposing a design range limit of approximately 4,500 NM.  This effectively curbs sales to airlines looking for SSTs to fly the pacific rim routes where the times savings offered by a supersonic aircraft would be the most pronounced.
Supersonic Flight Over Land Still Prohibited
Supersonic aircraft generate noxious sonic booms which can cause damage to fragile structures on the ground and generally are a nuisance to the inhabitants below.  While advancements in quiet supersonic transports are happening, global aeronautical regulation bodies still prohibit supersonic flight over land, restricting an SST to subsonic flight over these regions, making its operation exponentially more expensive than a traditional subsonic aircraft.
Concerns Over Safety Operating in Rarefied Atmosphere
A high speed SST would be required to operate in the higher parts of the stratosphere in excess of 60,000 feet.  While this is achievable for military pilots in full pressure suits, there are considerable risks to civilians in street clothes at these altitudes should a rapid decompression occur.  At these heights a rapid decompression will boil your blood inside your veins (very painful way to die).  It also cannot be combated with traditional supplemental oxygen systems, making such a scenario very dangerous for passengers.
Environmental Concerns
The 'dirty burning' turbojet previously discussed create a lot of NOX emissions, far more that today's high bypass turbofans, which poses risk of increased depletion of stratospheric ozone.
Cost Savings
A conventional high bypass turbofan subsonic airliner is between 16-20 times more efficient on a cost per passenger per NM basis. A typical transatlantic ticket on a 747-8 is approximately 1500 USD.  A ticket on the Concorde was about 11,000 in today's dollars.

Taken all together and faced with the reality of designing such a craft with 3 million parts, 6 million lines of software code, all tested and validated, which is restricted only to transatlantic routes, aircraft designers quickly see the handwriting on the wall and the aircraft is doomed from the drafting paper upward.
But that's not to say the supersonic dream is dead.  Aerion in Reno, NV and Airbus are in the process of developing a 16 passenger supersonic business jet, capable of Mach 1.6, with a tentative rollout and flight in 2021.  Areion claims the jet will have a 'boomless' cruise up to Mach 1.2 at or above FL350 and hopes this will coax regulating bodies into permitting supersonic flight over land.  Whether this attracts enough customers willing to pay the estimated $100 million price tag per aircraft remains to be seen.

Rapid decompression will not boil your blood at any altitude and not even outer space, because blood is pressurised to overpressure of around 80 mmHg by elasticity of the cardiovascular system and this pressure is enough to prevent it from boiling at normal body temperature. It will make your body swell a lot, any gasses in your gastrointestinal tract will expand and your skin, eyes and mucous membranes will quickly dry out, but none of that would be fatal. The biggest problem is that below ~15 kPa, even pure oxygen is not enough to breathe and you need pressure suit or at least mask.

Business aiming to build 45-seat supersonic airliners: "We're building the supersonic airliner anyone can afford to fly."

@JanHudec While your blood itself may not boil, the gases dissolved in it definitely will. Think of it as an extreme case of decompression sickness (the bends). The Soyuz 11 mission is an example of how rapid decompression can produce a very painful death.

@silvascientist, gasses are already gasses, they can't boil. They can release from the solution due to the reduced pressure (bends), but the pressures involved are small, so it would unlikely be fatal. All those effects certainly would be painful, but the fatal one is the lack of oxygen.

There are numerous reasons. They are not all economic ones by the way, even if most of them are.
First, you must build your supersonic airliner
Neither of the two supersonic airliners that once flew fly anymore, and none of the aircraft that still exist are likely to made airworthy ever again.
Someone's going to have to design and build a new one.
Unfortunately...
The historical moment has passed
The British and French governments began collaborating in earnest on the project in the late 1950s. The immediate post-war period was over, but they both faced a kind of crisis as their colonial empires fell apart across the world, making for just the kind of mood in which weakening global powers reach for grand projects that will prove that they really are, after all, in the top club of nations.
For slightly different reasons at the same time the USA and the USSR were also making huge efforts to prove themselves Top, expressed in the race to reach the moon.
It was at any rate a moment that seemed to demand extraordinary symbolic achievements in technology by certain governments.
Now, no government has the stomach for that kind of project, nor do their populations (one wonders whether China or India might soon decide that it's time for their grand gesture though). International agreements, such as those that bind the member states of the European Union as well as trade agreements that reach across the world, limit the kind of support governments can provide to enterprises of this scale, that made them possible in the past.
They don't seem to be able to keep their own airlines going any more, never mind global-scale technological extravagances.
So if the 21st century is no longer a time for such politically-powered technological extravagance, it's going to be up to private enterprise to produce it, and now the economic factors start to become more important.
A supersonic airliner is less necessary than it was
Time spent in the air is not "dead time" for the highly-expensive business traveller any more. Increasingly, in-flight Internet and telephone connections will make it less urgent to be there now. The business traveller will be more interested in comfort and facilities, if the flight time can be used productively.
Fluctuating oil prices are on everyone's mind
A supersonic airliner will be fuel-expensive. Since the 1970s, the price of oil has fluctuated violently enough several times to cause various airline-related extinctions. Airlines flying supersonic airliners will take the first hit.
And so is the environment
Airlines already face a great deal of pressure because of environmental concerns: it's an industry that's hugely damaging to the planet.
A supersonic airliner will be considerably more damaging than most.
Which airline is likely to want to be the first to fly the most environmentally-noxious airliner in the world in order for the super-rich to spend a little less time getting wherever it is they go?
Possibly, no airline could afford to buy it
It's far from clear that any airline could afford to invest in a supersonic fleet, and it would have to earn a vast amount of money even if they could.
It wouldn't be very useful
Where would it fly? One thing that the Concorde project failed to foresee was just how obnoxious the aircraft were to the people who lived anywhere near their noise.
For a while the British and French put up with the appalling noise it made because it reassured them that they were still great, but after a while even they grew pretty tired of it.
The Americans cared rather less about Franco-British greatness, and kept trying to ban it from the USA; it was banned from flying over various other places too.
Let's assume that you could build a supersonic airliner that was civilised enough to be reasonably welcome at airports near populous cities (and Concorde with its 1960s turbojets would not be), you'd still have an aircraft that could not be flown over populated land at supersonic speeds, because of the horrific noise its shockwave would make.
So, it would be pretty much limited to coast-to-coast operations over oceans.
In conclusion
There's not just one reason why we haven't seen a new supersonic passenger airliner, but a whole raft of them - and I think it will be a very long time before we do.

Another point is that supersonic flight, especially commercial supersonic flight, produces only marginal gains.  You might cut the actual flying time across the Atlantic, say, from 8 hours to 4, but the plane still spends the same time in taxiing & patterns, and the traveller still spends hours going through security, boarding, waiting for luggage, &c.  So what might be a 12 hour trip done subsonic becomes 8 hours supersonic.  Little gain for much greater cost.

@jamesqf Um, did you ever fly above the Atlantic in economy class in a subsonic airliner? My well-intended advice: don't do it! Wait for supersonic airliners to re-approach, or go by ocean liner.

@Giovanni: Yes, I have done that, which is why I know from experience that most of the trip time (and the less pleasant parts, IMHO) is spent on the ground, not flying.  And that was before the added time required for security theater.  These days, I certainly would take an ocean liner.

@jamesqf Anyway, flying faster shortens the time to get there, regardless of where you lose time. If you can half the travel time, you're still sooner on your goal. And if you go west-to-east, you would have flown fully in daytime in the Concorde.

@Giovanni: Sure, it shortens the trip, but most people wouldn't think the increased price (roughly 2X first class, or 10X full-fare coach) and discomfort (Concorde, like any SST, was cramped and noisy) was worth the small savings in trip time.  Honestly, if you're going to spend large amounts of money, wouldn't you rather have an extremely comfortable first class seat?  And then if you're not going from coastal airport to coastal airport, you have to switch planes, adding more time...

Re "...in-flight Internet and telephone connections will make it less urgent to be there now."  Indeed, as we've been learning during the current pandemic (or rather, as management has been forced to learn - most of us knew it long ago), there is really very little need to be THERE at all.  Just stay home and let the electrons do the travelling :-)

@jamesqf If supersonic travel became a standard rather than an exception (and supersonic flight was allowed over land), ticket prices would get the same as in current subsonic travel. But you're pretty right with your last statement. Such long-distance travelling is just unhealthy.

@Giovanni: No, the prices wouldn't be the same.  It takes a LOT more fuel to fly supersonic.  Then you have a more costly airframe, since it needs to be built to handle the extra stresses.

There are regulations in place that state that a supersonic aircraft can only go supersonic when over sea, (especially seen with concerns about noise levels when concorde was in production, and sonic booms 'breaking windows' when flying over land) and must be subsonic when on land, which limits the amount of destinations you could get supersonic flights to (like if you were travelling from Turkey to France), not to mention that supersonic jets guzzle fuel (especially delta winged design ones, such as Concorde and the TU-144, which need extra thrust on takeoff due to the design making it harder to gain lift).
They're very expensive to maintain as a whole, which can be seen by the amount of wear that can be done during supersonic flight, which is costly to repair, and if oil prices go up, it adds onto that expense because of how much it guzzles. If there's a demand for people to fly supersonic, then considering there's limited routes to do so, it would just make a supersonic jet a tin can of losses.

In addition to @DanieleProcida's great points, there is one more very significant factor affecting demand: long-range private jets.
Supersonic airliners only provide a speed benefit to passengers traveling between the cities directly served.  Once you have to connect (and go through customs and immigration, plus the inevitable schedule padding to minimize the risk of that causing missed connections), the end-to-end speed of the trip drops dramatically.  A long-range private jet can take you directly from origin to destination with no connection/layover time, and customs and immigration for GA aircraft is usually very fast.  Private jets can operate at much smaller GA airports that are likely to be much more convenient to the passengers, and there's no check-in lines or security theater adding time to the trip either.  They can also leave as soon as you get on board, rather than on a fixed schedule, though it is harder to calculate the dollar/time value of that.  And they're usually a heck of a lot more comfortable, with no worries about screaming kids and such--unless you brought your own.
Chartering a private jet is expensive, but one ticket on Concorde was in the same ballpark, and the private jet is definitely cheaper if several people are traveling together.

Although Concorde was still in good flying condition and a stellar plane,  when it was retired from service in 2003, it had been 34 years since it's first flight using technology that was first proposed in the 1950's There's simply not many planes that are still flying in commercial aviation that are more than 30 years old.
There's lots of reasons why supersonic transport never caught on. The reasons are far too many to list here and the most relevant ones have been covered in other answers. It gets down to economics. Neither the Tu-144 or the Concorde made economic sense beyond the limited routes they flew, which hampered anticipated sales.
Since the time the Concorde made it's first flight, there has been dramatic improvements in aerodynamics, electronics, engines and building materials. Most of the developments in aeronautics have been directed at improving planes flying below mach 1 for better fuel efficiency and noise reduction.  Some of those developments would work well for supersonic flight. Issues like sonic booms can be dramatically reduced which gives hope for overland flights. In some scenarios, the booms are reduced to 1% of what Concorde generated. If the planes can fly from New York to Seattle, then onto Tokyo, or trans Europe and Asia, it opens up entirely new markets that Concorde could not fly.
There have been efforts to bring back supersonic travel. Twenty years ago, Boeing proposed a faster plane, the Sonic Cruiser which would carry up to 250 passengers and have a sweet spot just below Mach 1 and just above Mach 1 and be much more economical to run. Commercial airlines didn't want extra speed so much as they wanted a plane that was cheaper to fly. This is how we ended up with the Boeing 787 Dreamliner instead.
However, there are several air-frames in development that are capable of supersonic flight. My strong feeling is that supersonic is coming back.
First off, Boeing never let the Sonic Cruiser concept die. I don't think they ever let go of the idea of a supersonic plane like the the Boeing 2707. Last year they announced a concept passenger plane capable of Mach 5.

For the last twenty years, EADS — the parent company of Airbus announced that it was considering working with Japanese companies to develop a larger, faster replacement for Concorde. The concept is a plane that carries 300 passengers at Mach 2 with a per-seat ticket price comparable to flying subsonic speeds. No firm plans have been announced.
Lockheed would like to get back into commercial aviation and has been working with Supersonic Aerospace International on a Quiet Supersonic Transport. This plane would seat 12 passengers, cruise at Mach 1.6 and create a sonic boom only 1% as strong as that generated by Concorde. It is also working with NASA on the X-59 QueSST.

Boom Technology is an American startup company designing a Mach 2.2 (1,300 kn; 2,300 km/h) 55-passenger supersonic transport with 4,500 nm (8,300 km) of range, to be introduced in 2023, called Overture. Boom is hoping to power the Overture with three moderate bypass turbofans without afterburners, unlike Concorde's Rolls-Royce/Snecma Olympus. The issue is finding a non-military efficient engine. Boom is working with Japan Airlines and Virgin to develop a plane that could make a flight from San Francisco to Tokyo in under 6 hours.

There are other planes in development. I think we are within five years of seeing supersonic planes capable of trans-atlantic, trans-pacific flights which should open up entire new markets for supersonic planes.


text:
Do aircraft use the same or similar warning alarms for different alarm conditions?
I was going through Helios crash and learned that Boeing was blamed for having similar sounding alarms for different alarm conditions.

On a given aircraft, can two different warning alarms have the same sound?
If so, what other aircraft have the same sound for different kinds of alarms?
Has Boeing changed their alarm systems post that incident?

Possible duplicate of Are the audible warning standardized?

@Manu H That question says are audible warning systems are standards across different aircrafts like Boeing/Airbus etc
but my question is more like do they creates similar type of sound for every alarm or have different kind of beep sounds for different kind of alarms?

quoted from this answer: "Even sounds within planes from the same manufacturer are different. The fire warning in a Boeing 737 sounds like a physical fire bell, while that on a Boeing 777 is an electronic "beep beep beep" sound.". I think your question as it is written now already has great pieces of answers in the answers of the question Are the audible warning standardized? and I encourage you to be more specific.

@NitinG I rephrased your answer based on your comment. Feel free to revert the edit if I didn't understand what you meant.

Has boeing changed their alarm systems post that incident?
The story of Helios Airways flight 522 is complicated. It is not clear that a misidentified alarm was the cause of the crash.
Update:
If you are talking about the cabin altitude warning horn, that was allegedly misidentified as a take-off configuration, then nothing has been changed, at least up to May 2015 (see: The Boeing 737 Technical Guide, Version 70, May 2015, bottom of the page 50).

"As the aircraft climbed, the pressure inside the cabin gradually decreased. As it passed through an altitude of 12,040 feet (3,670 m), the cabin altitude warning horn sounded. The warning should have prompted the crew to stop climbing, but it was misidentified by the crew as a take-off configuration warning, which signals that the aircraft is not ready for take-off, and can only sound on the ground.
  In the next few minutes, several warning lights on the overhead panel in the cockpit illuminated. One or both of the equipment cooling warning lights came on to indicate low airflow through the cooling fans (a result of the decreased air density), accompanied by the master caution light. The passenger oxygen light illuminated when, at an altitude of approximately 18,000 feet (5,500 m), the oxygen masks in the passenger cabin automatically deployed."m, Source: Helios Airways Flight 522.

and this would answer the question how?

Ur answer dont answer the question. This question doesnt say that what happened to Helios but asks if there are similar alarming alarms still in the cockpit?

If so, what other aircraft have the same sound for different kinds of alarms?

On older LR-JET typed learjets (31, 35, etc) the overspeed and cabin altitude warning sounds are eerily similar.  It hard to tell which one it is without verifying both airspeed indicators.